Primary carcinoma of ectopic axillary breast tissue.

The presence of ectopic breast tissue is reported in 2-6% of the general population with most cases being located in the axillary region. Although the same pathology occurs in both eutopic and ectopic breast tissue, primary carcinoma of ectopic breast tissue has been reported only in a small number of cases. Because an overlying accessory areola or nipple is often missing and because of a general lack of awareness among physicians and patients concerning these unsuspicious nodules, clinical diagnosis is frequently delayed. Histological diagnosis can also be delayed if ectopic breast tissue is not present or screened for in the biopsy specimens as apocrine glands of the breast and skin, respectively, exhibit striking similarities and immunohistochemistry is of limited help. Diagnostic delay is demonstrated by the case of a 56-year-old patient who underwent a series of four surgical excisions of a primary ectopic breast carcinoma and developed local lymph node metastasis until treatment with tamoxifen was started. As two-thirds of reported cases of primary ectopic breast carcinoma arose within the axillae, this case underlines the importance of a search for ectopic breast tissue in the context of axillary ductal carcinoma.